S-nitrosothiols (SNO) are stable, bioactive nitric oxide (NO) compounds found at high concentration in the lung. By inhibiting activation of the transcription factor NF-(B, SNO alters the immune response with evidence suggesting that fluctuation in airway SNO levels serves to regulate pulmonary inflammation. S-nitrosoglutathione reductase (GSNOR) and nitric oxide synthase (NOS) are enzymes that control lung SNO concentrations by increasing SNO metabolism and production respectively. In this regard, LPS-induced NF-(B activity and airway inflammation is augmented in the lungs of inducible NOS (NOS2)-null (KO) mice and diminished in the lungs of GSNOR KO mice. Furthermore, lung SNO repletion by ethyl nitrite (ENO) gas inhibits LPS-induced NF-(B activity and inflammation. Given these observations, we hypothesize that SNO serves to attenuate lung inflammation by inhibiting activity in the NF-(B pathway. To test this hypothesis, we have formulated the following specific aims: 1. Determine the importance of SNO metabolism in the regulation of lung inflammation. 2. Determine the role of SNO in modulating NF-(B signaling in the lung. 3. Investigate the effect of lung SNO repletion on lung inflammation and NF-(B activity. The pulmonary inflammatory response of C57BL6 wild-type (WT), NOS2 KO, NOS3 KO and GSNOR KO mice to aerosolized LPS will be contrasted. SNO levels (in the lung and airway fluid) will be quantified and correlated to pathological determinants of lung inflammation and NF-(B activity. The specific step(s) in the NF-(B signal transduction pathway that are sensitive to SNO will be identified and the proteins that regulate these steps analyzed for post-translational modification by S-nitrosylation. The effect of treatment with inhaled ENO and conventional NO gas on these parameters in LPS-exposed WT mice will also be examined. Accomplishing these aims will delineate the importance of SNO metabolism in the evolution of inflammation in response to lung injury and further elucidate the molecular mechanism(s) by which SNO modulates the immune response. These data could then translate into new therapeutic strategies in the treatment of acute lung injury. PUBLIC HEALTH RELEVANCE: Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) is a disease with an annual incidence in the United States of approximately 190,000 cases and a mortality rate between 40-50%. Despite its clinical significance, the pathophysiology of ALI/ARDS remains poorly understood with treatment limited to supportive care. This research proposal will address the importance of endogenously-produced molecules termed S-nitrosothiols, in controlling the inflammation that is associated with ALI/ARDS. The knowledge gained from the proposed studies could lead to the development of new therapies that target inflammation in ALI/ARDS and other pulmonary disorders..